1. Field of the Invention
The present invention generally relates to an electron source using a planar type cold cathode having tip end portions with a minute radius of curvature.
2. Description of Related Art
Conventionally, there have been proposed a large number of cold cathodes of the thin-film field emission type. Among these cathodes, a planar type cold cathode as shown in FIG. 6.(see, for example, Japanese Patent Laid-open Publication No. SHO 63-274047/1988) is said to be capable of generating electron emission at an applied voltage of 80 V or more. As shown in FIG. 6, this cold cathode is constituted by a cold cathode 24 arranged to confront an anode 25 on the surface of a substrate 23 of electrically insulating material. On the end face of the cold cathode confronting the anode, there are formed a large number of triangular convex portions each having a tip end portion with a minute radius of curvature by a microfabrication technique of submicron order. The distance between the tip end portions of the convex portions provided in said cold cathode and the anode is 0.1 .mu.m. When a voltage of 100 V or more is applied between said cold cathode thus constituted and the anode, because of the small radius of curvature of the tip end portion of each cold cathode, there is developed a strong electric field of 2.times.10.sup.7 V/cm at the tip end of each convex portion, resulting in field emission of electrons at the tip end portions.
Although said planar type cold cathode has an advantage as described above, it is necessary to make the radius of curvature at the tip end portion of the convex portions of the cold cathode as small as possible and to space the electrodes at a distance of submicron order. At present, however, according to the microfabrication method using a conventional photoetching technique, about, 0.7 .mu.m is the limit. Therefore, in order to perform a still smaller microfabrication, it is necessary to use a maskless etching technique such as FIB. According to this technique, however, it is difficult to form a cold cathode having a large area, and furthermore, this technique is not suitable for putting into practical use from the cost view-point in the manufacturing process.